Vapour discharge lamp



Aug. 20, 1957 J. JAUMANN ETAL 2,803,775

VAPOUR DISCHARGE LAMP Filed May 20, 1955 INVENTORS \fd/IA/V VES Jw/M/v BY Aa mm flan/400T United States Patent VAPOUR DISCHARGE LAMP Johannes Jaumann, Koln, and Konrad Ruthardt, Hanan (Main), Germany, assignors to W. C. Heraeus, G. in. b. H., Hanan (Main), Germany, a German body C01" porate Application May 20, 1955, Serial No. 509,976

6 Claims. (Cl. 313184) The present invention relates to a vapour discharge lamp which constitutes a considerable technical advance over the known discharge lamps.

Hitherto in practice gas discharge vessels have been used for lamps for the generation of visible light and of ultra-violet radiation, which contain vapours of readily volatile metals, more particularly mercury and cadmium, or a filling of rare gases (noble gases) and also hydrogen. It is often desirable, according to the particular intended application of the lamp, to obtain limitation of the radiated energy to certain spectral ranges in the visible spectrum or in the ultra-violet spectrum; it is therefore desirable to obtain lamps having as selective as possible a radiation.

In addition to the desired spectral distribution it is furthermore desirable that the supplied energy should to a large extent be delivered as radiation and only to a minor extent removed from the discharge path by conduction or convection, or in other words it is desirable to take care that the absolute emission power should be as high as possible.

The above mentioned discharge lamps do not yet satisfactorily comply with the said requirements, their emission being too small in the spectral ranges of interest as compared with the emission in other spectral ranges and with the loss by heat conduction and convection; for example the known high pressure mercury lamps will only emit about 6% of the supplied power as radiation in the pigment-forming ultra-violet A (315 to 400 mg) and approximately 12% in the visible spectral range. The loss by heat conduction and convection is roughly 75%, the cause residing above all in the concentration of the radiation to a few lines, the intensity of which cannot be increased at will by increasing the gas density.

It is an object of the present invention to provide gas discharge vessels which avoid the said drawbacks.

In order that the invention may be more readily understood, one embodiment of a vapour discharge lamp according to the present invention is illustrated in the accompanying drawing, one half of which is a section, while the other half is an elevation.

The lamp comprises a quartz envelope 1 having fusedin foils 2 by means of which current can be supplied to the electrodes 3. The discharge space 4 is according to the present invention filled with certain compounds under a predetermined pressure as will be explained in detail further below. Apart from this the electric circuits and the manner of operation of the vapour discharge lamp are as usual.

With the above mentioned object in view, the invention provides that oxides, or halides, or mixtures of oxides and halides, of metals of the 6th to 8th groups of the (old) periodic system (i. e. of the 4th to 8th groups of the transition series) are provided in the discharge vessel in such quantity that with the prevailing wall temperatures of the discharge vessel they have a vapour pressure suflicient for producing a pressure of more than 50 mm. Hg.

2,803,775 Patented Aug. 20, 1957 According to one aspect of the invention the discharge vessel is preferably equipped with fixed solid electrodes and is generally operated with the hitherto usual voltages, but instead of being filled with a volatile element such as mercury, it is filled with such compounds of an element which is non-volatile in itself and which in the required range of the visible spectrum or the ultra-violet spectrum has strong emission, which at the wall temperatures of the discharge vessel develop a vapour pressure of, for example, 50 mm. Hg to 3 atmospheres, sufficient for the required discharge pressure, more particularly of a high pressure discharge. Thus, when employing for example quartz glass for the envelope of the discharge vessel, such compounds are chosen, in the form of the oxides or halides of the metals of the 6th to 8th groups of the (old) period system as are so volatile that at temperatures below approximately 800 to 1000 C. the required vapour pressure prevails. Thus when, for example the wall temperature of a quartz vessel is less than 800 C. at the hottest point and according to the particular arrangement, for example between and 700 C. at the cool-est point, the operating pressure is above 50 mm. Hg. The characteristic features of the invention are more particularly in appearance in high pressure discharges. High pressure discharge offers advantages since for most applications the size of the discharge vessels must not exceed a predetermined dimen sion, and since in a quartz vessel of limited size it is impossible at low pressure to obtain adequate radiation power.

While a sufiicient amount of elementary substance is present in the hot discharge core for the emission of the atomic spectrum, the compound remains stable near the hot wall.

If in certain cases, in spite of these conditions which are particularly favourable in the gas plasma, the equilibrium is, even in the border zone, too far on the side of the compound components, decomposition may be counteracted by increasing the proportion of the compound component complementary to the spectrally active substance, that is to say by increasing the concentration of oxygen or halogen or both. An excess of the latter will in some cases also establish itself automatically by deposition of the excess metal at parts of these vessels free from plasma, that is to say at a point which is innocuous for the light exit of the radiation. Otherwise an extra addition is sufiicient which generally is less than 50% and in many cases even less than 10% of the pressure to be obtained of the compound, and need only in rare cases exceed the pressure of the latter.

Most of the metals of the 6th to 8th groups of the (old) periodic system emit with preference radiation throughout the whole of the ultra-violet path of the spectrum, especially when an alternating current discharge is used.

Some examples shall be given by way of explanation.

If the discharge is effected with a current of between 0.5 and 5 amps. and a vapour pressure of rhenium heptoxyd is produced which, at a temperature of the discharge vessel of 800 C. at the hottest point and of 300 C. at the coolest point, is between of an atmosphere and 1 atmosphere, densities of light up to 100,000 Stilb. are obtained.

Similar increases of output are obtained with osmium textroxide which may, for example, be used at a vapour pressure of 0.1 to 1 atmosphere. In the case of low pressures, an addition of oxygen is preferably provided, for example an addition of 10 mm. Hg oxygen in the case of a pressure of 50 mm. Hg of osmium textroxide. In this case, too, the temperature of the hottest point of the discharge vessel may, for example, be 800 C. and that of the coolest point for example 100 C. Under these conditions densities of light emission up to 100,000

Stilb. may likewise be attained. With the said osmium tcxtroxide of 50 mm. Hg with the addition of 10 mm. Hg of oxygen an ultra-violet spectrum is obtained which is extremely rich in lines, has constant energy down to nearly 220 [Tl/L, and within the ultra-violet A shows the same radiation power per centimetre of discharge space as a usual high pressure mercury lamp. Added to this is a strong continuum in the long-wave ultra-violet and in the visible spectrum, which imparts to the discharge a sun-like white appearance.

These substances thus show the more or less sun-like continuum. In all these cases the intensity of all lines increases considerably with increasing vapour pressure.

If a discharge in a vapour of molybdenum oxide M003 of about 0.1 atmosphere is maintained with a current strength of l to 5 amps. in a discharge vessel of which the hottest point is 800 C. while its coldest point is at 700 C., somewhat lower densities of light emission are obtained than in the preceding examples.

The halides of the metals of the 6th to 8th groups of the (old) periodic system (4th to 8th groups of the transition series) will produce a similar effect as the oxides. In this case, too, the highest valency stages of the elements in question are suitable, that is to say those valencies which correspond to the group number of the element in question in the (old) periodic system. Amongst the halides the chlorides are more particularly suitable, but in addition also the other halides. Com pounds of the metals of the said 6th to 8th groups containing two different halogens at the same time are also suitable.

Iodides have the advantage that there are amongst them electron-emitting substances for the activation of the electrodes, so that in this case interaction between the activated electrode and the compound component need not be feared.

Amongst the halides of the 8th group of the (old) periodic system the halides of platinum metals may be mentioned, and amongst metals of the 6th group of the periodic system also the violet chromium chloride.

In the case of the halides, too, the surprising observation was made that in the case of compounds with which from the point of view of the chemist complete decomposition might have been expected at the high plasma temperatures, the quantities can be so chosen that a state of equilibrium with a sufficient proportion of the volatile compounds is obtained. In this case, too, the equilibrium can be established in any case by a suitable addition of the complementary participant of the reaction.

For completeness sake we will also point out that those metals of the 6th to 8th groups of the (old) periodic system of which the oxides or halides are employed according to the present invention, are found in the side rows of the groups in question, or in other words all these metals will be found in the 4th to 8th groups of the transition series.

In order to initiate the discharge, the usual ignition assisting means may be employed, for example auxiliary electrodes and additional introduction of an inert gas, but in many cases the excess provision of the compound component complementary to the element spectrally utilised, that is to say the excess of oxygen or of the halogen, is sufiicient for this purpose.

Suitable for use as electrodes are the known highly refractory metals such as tungsten, and semiconductors such as carbides and oxides, the emission being activated by known substances. Activated alkaline-earth metal electrodes are, it is true, in many cases alfected in their action by the complementary element of the compound. In this case one will have to be satisfied with the weakly emitting action of the non-activated oxide but, as already mentioned, there are also activators such as iron iodide, which are resistant to an atmosphere of halides and halogens.

The discharge vessels of the invention consist preferably of quartz glass and if desired of the other tempera ture resistant materials known for discharge vessels, more particularly high-melting glasses.

The shape of the vessels may be either the known tube shape or, in cases in which the high gradient of the discharge produces a short discharge and an excessive power per unit of length, spherical shape. Moreover the intensity distribution within the spectrum may be influenced according to requirements by suitably choosing the diameter of the discharge vessel, when the molecule shows selective absorption in individual parts of the spectrum.

Where the natural air cooling of the shape of the vessel is insuflicient for establishing the required operating temperature and the vapour pressure, cooling of the discharge vessel is effected in a known manner. When the temperature is too low, the colder parts of the discharge vessel are thermally insulated.

By the temperature control of the wall of the discharge vessel, that is to say more particularly by the choice of cooling conditions and heat insulation and by the choice of the shape and size of the vessel-a smaller surface will become hotter than a larger surface other conditions being equal-one is enabled to raise the operation from a low-pressure discharge to a high-pressure discharge or even to a very-high pressure discharge.

Summing up it will be seen that by the selection of compounds of the metals of the 6th to 8th groups of the (old) periodic system (4th to 8th groups of the transition series) the range of the elements suitable for spectral excitation in the visible and more particularly in the ultra-violet range can be considerably increased. It is more particularly made possible to exploit the line-rich spectra of the various elements which in application are equivalent to a continuum.

For the various ranges of the ultra-violet spectrum the oxides and halides of rhuthenium, rhodium, palladium, cobalt, nickel, rhenium, molybdenum, and besides these also those of iridium, osmium, platinum, chromium, and tungsten are according to the invention employed with particular advantage. If desired mixtures of compounds of different metals may be employed.

As far as the visible spectrum is concerned, white light is produced in some cases and light of a predetermined colour in other cases; by the combination of compounds of different elements the spectral ranges may be supplemented according to requirement.

A number of the elements of the higher groups show, more particularly at higher vapour pressures, an intensive continuous spectrum in the visible spectrum and in the long-wave ultra-violet, so that these elements are suitable as an economical light source for pure-white light. One has thus available a simple method of producing a more or less sun-like spectrum.

In the case of some difticultly volatile emitting elements partial condensation may take place in the form of an aerosol, which then produces a desired intensification of the continuum. The element then takes over the same function as the finely distributed carbon in a luminous flame. In the colder parts of the discharge vessel the element is then reconverted into the compound.

It at individual points of the discharge the critical temperatures are exceeded or dissociation takes place, this does not affect the preceding considerations although in such a case we are strictly speaking concerned by gasdischarge lamps and not with vapour-discharge lamps. Such gas-discharge lamps are intended to be included in the cover of the claims of the present specification.

For the execution of the invention generally discharge vessels equipped with electrodes are employed, since in practice an electrode-less excitation with high frequency is too complicated and expensive. By the invention the spectral emission of certain elements is particularly favourably exploited which in themselves are not sufficiently volatile. Moreover it is emphasised once more that the invention does not produce by means of more or less instable compounds a gas pressure for the existence range of a few mm. Hg, but that it is concerned with producing substantial pressures, namely pressures of more than 50 mm. Hg, i. e. pressures for the high-pressure range, for industrially useful periods of operation. By this our discharge lamp is distinguished from laboratory arrangements intended for scientific investigations relating to short-period electric discharges for the study of the spectra of the elements, in which no radiation-technical consid erations arise. Since in contrast to the ancient are lamps equipped with movable electrodes, the preferred embodiment of the invention relates to high-pressure lamps (quartz lamps) which in the known manner ignite with fixed electrodes at low pressures and produce themselves gradually their high vapour pressure, no substances which have already at room temperatures so high a vapour pressure that ignition is impossible at the normal operating voltages, are employed for the filling according to the invention. On the contrary the compounds are chosen from the range of the above mentioned substances.

We claim:

1. In a vapour discharge lamp comprising a discharge envelope containing spaced electrodes, a filling material selected from the group consisting of oxides and halides of metals of the 6th to 8th group of the periodic table, said filling material being contained in said envelope in an amount sufficient to provide a vapour pressure above 50 mm. Hg at the operating wall temperatures of said envelope.

2. In a vapour discharge lamp comprising a discharge envelope containing spaced electrodes, a filling material the main component of which is at least one compound selected from the group consisting of oxides and halides of metals of the 6th to 8th group of the periodic table, said filling material being contained in said envelope in an amount sufficient to provide a vapour pressure above 50 mm. Hg at the operating wall temperatures of said envelope.

3. In a vapour discharge lamp according to claim 2. wherein said electrodes are semi-conductors.

4. In a vapour discharge lamp according to claim 2. wherein said envelope contains in addition to said compound an excess of at least one non-metallic compound of said groups and in such quantitive ratio with the metal compound that the vapour pressure of the lamp filling is more than 50 mm. Hg.

5. Vapour discharge lamp comprising a discharge vcssel equipped with fixed electrodes, and a filling in said vessel including at least as its main component, compounds chosen from the group comprising oxides and halides of metals of the 6th to 8th groups of the periodic system, in which said metal is present in its highest valency stage, corresponding to the group number, the Walls of said Vessel consisting of quartz glass and having such a temperature that the vapour pressure of the compounds is between 50 mm. Hg and 3 atmospheres.

6. Vapour discharge lamp for the production of rndiation having sun-type spectral characteristics in at least a partial range of the spectral range including the visible spectrum and the ultra-violet comprising a discharge ves sel, and a filling in said vessel consisting of at least one compound chosen from the group comprising oxides and halides of metals of the 6th to 8th groups of the periodic system the vapour pressures of said compounds being adjusted to pressures above 50 mm. Hg under the predetermined discharge conditions according to the Wall temperature of the discharge vessel said temperature being controlled by cooling and heat insulation.

References Cited in the file of this patent UNITED STATES PATENTS 2,697,183 Neunhoeffer et a1. Dec. 14, 1954 

1. IN A VAPOUR DISCHARGE LAMP COMPRISING A DISCHARGE ENVELOPE CONTAINING SPACED ELECTRODES, A FILLING MATERIAL SELECTED FROM THE GROUP CONSISTING OF OXIDES AND HALIDES OF METALS OF THE 6TH TO 8TH GROUP OF THE PERIODIC TABLE, SAID FILLING MATERIAL BEING CONTAINED IN SAID ENVELOPE IN AN AMOUNT SUFFICIENT TO PROVIDE A VAPOUR PRESSURE ABOVE 50 